Method for converting hydrocarbons



Patented Nov. 19,1946

METHOD FOR CONVERTING HYDROCARBON S Hillis 0. Folkins, Skokie, andCarlisle M. Thackcr, Highland Park, IlL, assignors to The Pure OilCompany, Chicago, Ill., a corporation of Ohio No Drawing. ApplicationOctober 31, 1945, Serial No. 625,938

16 Claims. 1

This invention relates tothe conversion of hydrocarbons and moreparticularly to the cracking of hydrocarbons containing three or morecarbon atoms per molecule to hydrocarbons of lower boiling point or tohydrocarbons of higher degree of unsaturation.

This application is a continuation-in-part of application Serial No.520,536, filed January 31, 1944, entitled Method for convertinghydrocarbons.

We have discovered that esters, and particularly esters of aliphaticalcohols and fatty acids, in which one or more bromine atoms aresubstituted for one or more hydrogen atoms, are efiective as sensitizersin accelerating the decomposition of hydrocarbons when the brominatedester is present in the reaction zone in small amounts. Examples ofbrominated esters which may be used in accordance with our inventionare: methyl bromoacetate, ethyl bromoacetate, ,3- bromoethyl acetate,ethyl dibromoacetate, bromomethyl acetate, ethyl-a-bromo-n-butyrate,ethyla-bromo-iso-butyrate, ethyl-u-bromopropionate,

ethyl-p-bromopropionate, methyl-a, ,B-dibromopropionate,methyl-s-bromopropionate, 5-bromon-propyl acetate. Esters of inorganicacids, such as di-octyl acid pyrophosphate, in which bromine issubstituted for one or more hydrogen atoms, may be used. Compoundscontaining more than one bromine atom are preferred over compounds whichcontain only one bromine atom since the poly-brominated esters are moreactive. The brominated ester may be added to the charging stock beforecharging it to the heating and conversion zone or it may be injecteddirectly into the conversion zone. Brominated esters are effective ascracking accelerators or sensitizers in in amounts equivalent to 0.001to 0.1% of bromine by weight give a greater increase in yield amountsequivalent to as low as 0.001% by weight of bromine based on thecharging stock. Amounts between 0.005 and 3% by weight of sensitizer maybe used effectively, although larger amounts may be used if desired. Weprefer not to use amounts in excess of 3% by weight since amounts below3% will provide satisfactory acceleration of the cracking reactionWithout causing the presence of of gasoline boiling hydrocarbons perunit weight of sensitizer than is obtained with larger amounts. In otherwords, although the yield of cracked asoline increases up to a certainpoint with increase in the amount of sensitizer used, the increase isnot sumciently great to justify the use of larger amounts.

Sensitizers, in accordance with our invention,

are useful in thermal cracking processes at either subatmospheric,atmospheric, or super-atmospheric pressure. Cracking of hydrocarbon oilsand/or gases may be carried out with brominated esters at temperaturesof approximately 650 to '2000 F., depending upon the nature of thecharging stockand the type of product desired. Where cracking ofhydrocarbon oils to gasoline is practiced, the temperature may rangefrom approximately 650 to 1200 F. When gases or oils are 1 cracked toaromatic hydrocarbons, temperatures of approximately 1000 to 1500 F. maybe resorted to. When it is desired to crack hydrocarbon oils or gases tobutadiene, temperatures of the order of 1300 to 1600 F. may be used.Where cracking of oils or gases to lower molecular weight gaseoushydrocarbons is practiced, such as, cracking of propane to ethylene,temperatures of 1200 to 2000 F. may be used.

In carrying out our invention, we prefer to use brominated esters whichare volatile at reaction temperatures. Where brominated esters are usedwhich are unstable at temperatures at or below cracking temperature, itmay be desirable to in- ,iect the sensitizer directly into the reactionzone in order to prevent decomposition thereof before the cracking stockwith which it is mixed reaches cracking temperature.

In order to demonstrate the effectiveness of brominated esters ascracking sensitizers, a number of runs was made in a Pyrex glassreaction vessel at 977 F. using butane of 99% purity as charging stock.Each run was made by heating the reaction vessel to 977 F. andevacuating the vessel by means of a vacuum pump to a pressure of 0.001millimeter of mercury. Butane when mixed with the desired amount ofsensitizer was then charged to the evacuated vessel until the pressuretherein was approximately atmospheric.

Readings were made as to the time required to attain a pressure increaseof 12.5%, and 25%. When the pressure increase had reached 25% thereaction products were rapidly evacuated from the vessel and analyzed.

A number of runs was also made in the same manner without anysensitizers to enable a comparison to be made in the acceleration ratewith and without the sensitizer. Data for the various runs are tabulatedin the following table:

2. Method in accordance with claim 1 in which the brominated estercontains at least two bromine atoms.

3. Method in accordance with claim 1 in which the ester is an ester ofan aliphatic alcohol and fatty acid in which bromine is substituted forhydrogen.

4. The method of cracking hydrocarbons having at least three carbonatoms in the molecule Table Initial Sensitizcr Run N 0. pressure Time inminutes for g g lfiff Mole per cent reaction products cm. Hg

Name Per cent 5% 25% Acids Unsat. O0 Residue 82. Methyl bromo acetate.0. 5 0. 39 1. 04 2. 97 5. 1 7. 5 7. 4 0. 2 24. 3 0. 4 1. 3 73. 8

81. 90 Methyl bromo acetate. 0. 0. 43 1. 24 3. 63 4. 6 6. 3 6. 0 0.0 24.1 0. 2 1. 2 74. 5

82. Methyl bromo acetate. 0. 25 0. 52 1. 40 3. 97 3. 8 5. 5 5. 5 0. 224. 0 0. 2 1. 2 74. 4

Ethyl bromo actate.

Ethyl bromo acetate.

Sensitization factor is obtained by dividing the time required to attaina given pressure increase without sensitizer by the time required toattain the same pressure increase with sensitizer. The average offigures for non-sensitized runs appearing in the table immediatelybefore the sensitized runs is used as a basis for determiningsensitization factor.

From the table it Will be seen that ethyl and methyl bromo acetate andp-bromo-ethyl-acetate accelerated the reaction to a considerable extent.Of the brominated esters appearing in the table, methyl-bromo-acetate isthe most effective.

Although our invention is applicable to all known types of hydrocarboncracking processes, catalytic and purely thermal, it is particularlyadapted for use in purely thermal operations in which no solid catalystis used. The invention may be adapted to present types of thermalcracking processes without modifying operation or apparatus in whichthey are conducted, except to the extent to provide for the addition ofthe sensitizer to the charging stock or to the reaction vessel.

We claim:

1. The method of cracking hydrocarbons which comprises subjecting saidhydrocarbons to suitable cracking conditions of time, temperature andpressure in the presence of a small amount of a brominated ester.

8020160115 2.08 7.83 '21.e1 0.1 22.4 0.1 1.4 70.0 79.95 B-Bromo-ethylacetate. 0.5 0.60 2.68 7.83 3.2 2.9 2.8 0.0 23.0 0.0 1.3 75.7 81.fi-Bromo'ethylacetate. 0.25 0.74 3.05 8.70 2.8 2.6 2.5 0.1 22.7 0.2 1.275.8

to lower boiling hydrocarbons which comprises subjecting saidhydrocarbons to temperatures of 650 F. to 2000" F. in the presence of asmall amount of an organic acid ester in which bromine is substitutedfor at least one hydrogen atom.

5. Method in accordance with claim 4 in which the amount of brominatedester present in the mixture undergoing reaction is between 0.005 and 3%by weight.

6. Method in accordance with claim 4 in which the amount of brominatedester present in the mixture undergoing reaction is between .005 and 1%by weight.

7. Method in accordance with claim 4 in which the amount of brominatedester present in the mixture undergoing reaction is not in excess of 1%by Weight.

8. Method in accordance with claim 4 in which the hydrocarbons comprisea large portion of propane.

9. Method in accordance with claim 4 in which the brominated ester ismethyl bromoacetate;

10. Method in accordance with claim 4' in which the brominated ester isethyl bromoacetate.

11. Method in accordance with claim 4 in which the brominated ester isp-bromoethyl acetate.

12. The method of cracking hydrocarbons having at least three carbonatoms to the molecule which consists in subjecting said hydrocarbons tothermal cracking temperature in the presence of approximately from 0.005to 3% by weight of a brominated ester.

13. The method of cracking hydrocarbon liquids to gasoline boilinghydrocarbons comprising subjecting said hydrocarbon liquids to suitablecracking conditions of time and temperature in the presence ofsuflicient brominated ester to accelerate the rate of cracking but notin excess of an amount equivalent to about 0.1% by weight of bromine.

14. Method in accordance with claim 13 in which the brominated ester ispresent in an amount equivalent to about 0.001 to 0.1% by weight ofbromine.

6 15. The method of cracking hydrocarbon oil boiling above the gasolinerange to hydrocarbons boiling within the gasoline range comprisingsubjecting said oil to temperatures of approximately 650 to 1200 F. inthe presence of an amount of brominated ester suflicient to acceleratethe rate of cracking but less than an amount equivalent to 0.1% byweight of bromine.

16. Method in accordance with claim 15 in 10 which ester is apolybrominated ester.

HILLIS o. FOLKINS. CARLISLE M. THACKER.

